This invention relates to conveying equipment and more particularly to tripper conveyor systems used, for instance, in the mining, aggregate, agriculture, cement, waste management, and construction industries.
A tripper is a type of industrial conveyor typically used in construction, mining, and other large-scale earth-moving businesses. For example, trippers may be used in conjunction with overland conveyor systems for mobile stacking of leach pads and storage piles. Such trippers uniformly spread mined material at variable heights over a predetermined area, facilitating leaching processes. Also known as a “tiered conveyor” or a “stepped conveyor”, a tripper provides flexibility within mobile materials handling systems as it rides on rails provided on a conveyor frame and travels forward or backward along the conveyor as needed. This allows the tripper conveyor system to load material onto a selected loading area of a transportation vessel or stacking/storage pile. Tripper conveyor systems are typically constructed of steel with solid trolley wheels, a rubber lagged drive roller, heavy-duty bearings on rollers, and a belt resting on said rollers which typically range from 36 to 96 inches in width and up to several miles in length. For longer belt tripper conveyor systems, the conveyor may be formed by hinging multiple conveyor frame sections together. Belts may include tall ridges or flaps affixed laterally to their faces in order to keep transported materials from sliding back down the conveyor. Trippers typically comprise a pulley system which maintains tension on the belt regardless of its position with respect to the conveyor frame, and a transverse belt which changes the direction of material to be generally perpendicular to the conveyor. Eventually, the material discharges from the transverse belt a distance away from the conveyor. Multiple electric motors coupled with a motor brake are used to move and stop the tripper car.
To this end, there are generally two types of drive systems for trippers: standard (friction) induction drives, and capstan (cable/pulley) drives. Standard induction drives are typically overhead crane wheel assemblies which are fitted to the tripper chassis. They rely on the weight of the tripper and friction-induced traction between the conveyor rails and the tripper wheels to move and stop. Capstan drives typically rely on cable tension and friction between the cable and a complicated system of motor-driven sheaves to move the tripper.
Some mining work sites require tripper conveyor systems to operate on slopes that exceed the recommended limit of 7% grade (4 degree angle slope) for standard induction drives. In these situations, manufacturers normally eliminate the direct wheel drives, and use non-driven idle crane wheel assemblies in combination with capstan drives, pulleys, and specially-designed cables (e.g., with plastic inner core and outer braided wire strands/fibers).
Problems associated with the abovementioned conventional tripper drives are numerous. For instance, as suggested in FIG. 21, standard induction drives are not recommended to operate with wheel rails 816 inclined greater than 7% grade (approximately 4 degrees from horizontal). Particularly in adverse weather conditions or high dust environments inherent to mining operations, higher inclination angles might not be possible to do decreased friction between the conveyor wheel rails 816 and trolley wheels. Such limits reduce the mobility and versatility of a tripper conveyor system. Moreover, when using standard induction drives, if the tripper brakes fail, the tripper may not stop when in a parked position, causing a potential hazardous “sliding” situation. Lastly, delays in starting, stopping, and reversing movement of the tripper as well as “wheel slip”, “sliding”, or “spinning out” may be experienced as a result of constantly changing coefficients of friction between the drive wheels and wheel rail 816.
Moreover, while capstan drive systems afford greater operational inclination angles than standard induction drives, they are expensive and require expensive, specially-designed, cables which need to be replaced approximately every six months. The cables are constantly exposed to high abrasion, rely on a coefficient of friction that is dependent on cable tension, attract dirt when greased, and tend to stretch under heavy loads thereby providing a delayed or indiscernible starting and stopping response when moving or reversing the tripper. Delays in starting, stopping, and reversing movement of the tripper as well as “wheel slip”, “sliding”, or “spinning out” may be experienced as a result of dirt, dust, or debris getting caught in circumferential grooves between the pulleys, and the cable.
Moreover, while cable lengths can be shortened, they cannot be elongated without changing the uniformity of cable properties. Therefore, capstan drives lack total mobility and versatility because conveyors must be kept the same predetermined length for the life of the cable, unless the tripper conveyor system is shut down temporarily for cable maintenance, adjustment, or replacement. Additionally, when it comes to “retrofitting” a tripper for use in steeper grades and rough terrain, a capstan upgrade is not typically a good option, since conveyor frames for use with capstan drives are typically initially made wider to accommodate and protect cables and also to allow some small misalignment between multiple conveyor sections without significant penalty (e.g., cable abrasion).
Capstan cables are typically tensioned from one end of a linked assembly of conveyor frame sections to an opposite end of the linked assembly, and conveyor frame sections tend to meander back and forth to some degree between these two endpoints while in operation. Therefore, especially in instances of significant terrain or inadvertent movement of conveyor frame sections, relative angles between hinged conveyor frame sections can become so severe that the cable can become slack or even severed between the wheels and wheel rail 816. For example, in some instances, multiple conveyor frame sections may form a curved conveyor profile, wherein the cable is taught and follows a straight cable path or the cable is slack and meandering over the rail which leads to wear. Such instances may pose great safety concerns for operators and increased risks to investors regarding unscheduled downtime for repairs and unexpected capital/maintenance costs. Moreover, if a cable fails while under tension, it can become an extremely dangerous moving object for nearby operators.